Role of atomic bonding for compound and glass formation in Ni-Si, Pd-Si, and Ni-B systems.

Abstract

Valence electronic structures of crystalline compounds and glassy alloys of Ni silicides, Pd silicides, and Ni borides are studied by soft-x-ray spectroscopy over wide ranges of Si and B concentrations. The samples prepared include bulk compounds, glassy ribbons, and amorphous sputtered films. Silicon K\ensuremath{\beta} emissions of Ni and Pd silicides generally consist of a prominent peak fixed at \ensuremath{\approxeq}4.5 and \ensuremath{\approxeq}5.8 eV below the Fermi level ${E}_{F}$, respectively, with a shoulder near ${E}_{F}$ which grows and shifts toward lower energy with increasing Si concentration. The former is identified as due to Si p\char21{}like states forming Si 3p\char21{}Ni 3d or Si 3p\char21{}Pd 4d bonding states while the latter as due to the corresponding antibonding states. Ni ${L}_{3}$ and Pd ${L}_{3}$ emissions of these silicides indicate that Ni 3d and Pd 4d states lie between the above two states. These local electronic configurations are consistent with partial-density-of-states (PDOS) calculations performed by Bisi and Calandra. Similar electronic configurations are suggested for Ni borides from B K\ensuremath{\alpha} and Ni ${L}_{3}$ emissions. Differences of emission spectra between compounds and glasses of similar compositions are rather small, but some enhancement of the contribution of antibonding states to the PDOS near ${E}_{F}$ is suggested for certain glasses over that of the corresponding compounds. These features are discussed in connection with the compound stability and glass formability.